1. Field of the Invention
The present invention relates to a screw for dental implants and, more particularly, to an improved screw for dental implants, used for fitting dental prostheses by tightening to abutments combined with fixtures previously inserted in alveolar bones and facilitating manipulation of the screw.
2. Discussion of the Related Art
FIG. 1 is a side view of a screw for dental implants in accordance with a contemporary art. FIG. 2 is a longitudinal cross-sectional view of a screw for dental implants shown in FIG. 1, wherein the screw is shown in a tightened state of use with respect to associative components.
Referring to FIGS. 1 and 2, a dental-implant screw 2 is a screw used for fitting a dental prosthesis 10 to an abutment 8. The abutment 8 is coupled to a fixture 6, which has been coupled with an alveolar bone 4.
The fixture 6 comprises a knurled portion 12 inserted as an anchor into the alveolar bone 4, a fixing hole 14 formed to prevent the fixture 6 from moving above the upper end of the knurled portion 12, and a first female-threaded portion 16 to receive the abutment 8.
The abutment 8 comprises a first male-threaded portion 18 formed at the lower end thereof and screwed into the first female-threaded portion 16 of the fixture 6, and a body portion 20 tapered to facilitate the fitting of the dental prosthesis 10. Further, the body portion 20 of the abutment 8 comprises a second female-threaded portion 22 for receiving the screw 2.
The screw 2 comprises a second male-threaded portion 24, formed to be inserted into the second female-threaded portion 22, and a screw-head portion 28 having a recess 26 to be manipulated using a tool such as a screwdriver.
The upper face of the screw-head portion 28 of the screw 2 is formed as a flat plane, and the recess 26 of the screw-head portion 28 is formed as a hexagon, a rectangle, or a slot-shape to be tightened by the tool.
The screw 2 is coupled to the abutment 8 via a penetration hole 30 formed in the dental prosthesis 10, so that the dental prosthesis 10 is fixed firmly.
To tighten the screw 2 in the penetration hole 30, the tip of the tool should fit in the recess 26 to enable the screw 2 to be turned by force. Due to the complex shapes of dental prostheses and spatial restrictions of the oral cavity, however, fitting the tool in the recess is difficult and manipulating the tool within the limited space is cumbersome.
In other words, since the space of the oral cavity is very limited, it is difficult to fit the tool into the recess 26 of the screw-head portion 28 of the screw 2 inserted in the penetration hole 30 formed in the dental prosthesis 10. Thus, repeated attempts to fit the tool in the recess 26 and turn the screw 2 are often necessary, because the upper face of the screw-head portion is flat. Accordingly, the tool cannot be guided into the recess 26, and on occasion, slides off the upper face. As a result, the screw 2 cannot be tightened promptly, and when tightened by an immoderate torque, the surrounding portions of the recess 26 are easily dulled by the tool.
The conventional screw for dental implants exhibits several further disadvantages: when inserted in the penetration hole 30 of the dental prosthesis 10, the screw 2 is difficult to locate visually, which hinders manipulation of the screw 12; if the surrounding portions of the recess 26 of the screw 2 become dull, the screw can be untightened only after breaking down the dental prosthesis 10, which necessitates remaking the dental prosthesis 10; the reduction of the clamping force of a tightened screw 2, due to the normal masticatory operation of the dental prosthesis 10, results in a loosening of the dental prosthesis, allowing undue movement; and a repetitive manipulation of the screw 2, e.g., tightening and untightening, is required for regular cleaning of the fitted dental prosthesis 10, but in retightening the screw 2 after a cleaning operation, the required clamping force is difficult to achieve if the tightening and untightening have been performed by compulsion, such that the surrounding portions of the recess 26 of the screw 2 become dull.